Demonstration of conditional quantum phase shift between ions in a solid

Due to their potential for long coherence times, dopant ions have long been considered promising candidates for scalable solid state quantum computing. However, the demonstration of two qubit operation has proven to be problematic, largely due to the difficulty of addressing closely spaced ions. Here we use optically active ions and optical frequency addressing to demonstrate a conditional phase shift between two qubits

Theory of Direct Scattering, Trapping and Desorption in Atom-Surface Collisions

When gas atoms or molecules collide with clean and ordered surfaces, under many circumstances the energy-resolved scattering spectra exhibit two clearly distinct features due to direct scattering and to trapping in the physisorption well with subsequent desorption. James Clerk Maxwell is credited with being the first to describe this situation by invoking the simple assumption that when an impinging gas beam is scattered from a surface it can be divided into a part that exchanges no energy and specularly reflects and another part that equilibrates or accommodates completely and then desorbs with an equilibrium distribution. In this paper a scattering theory is developed, using an iterative algorithm and classical mechanics for the collision process, that describes both direct scattering and trapping-desorption of the incident beam. The initially trapped fraction of particles can be followed as they continue to make further interactions with the surface until they are all eventually promoted back into the positive energy continuum and leave the surface region. Consequently, this theory allows a rigorous test of the Maxwell assumption and determines the conditions under which it is valid. The theory also gives quantitative explanations of recent experimental measurements which exhibit both a direct scattering contribution and a trapping-desorption fraction in the energy-resolved spectra.Comment: 46 pages including 14 figure

Phase-dependent decoherence of optical transitions in Pr3+:LaF3 in the presence of a driving field

The decoherence times of orthogonally phased components of the optical transition dipole moment in a two-level system have been observed to differ by an order of magnitude. This phase anisotropy is observed in coherent transient experiments where an optical driving field is present during extended periods of decoherence. The decoherence time of the component of the dipole moment in phase with the driving field is extended compared to T_2, obtained from two-pulse photon echoes, in analogy with the spin locking technique of NMR.Comment: 5 pages, 2 figures; replaced with published versio

Modifying molecular scattering from rough solid surfaces using ultrashort laser pulses

We consider solid surface scattering of molecules that were subject to strong non-resonant ultrashort laser pulses just before hitting the surface. The pulses modify the rotational states of the molecules, causing their field free alignment, or a rotation with a preferred sense. We show that field-free laser-induced molecular alignment leads to correlations between the scattering angle and the sense of rotation of the scattered molecules. Moreover, by controlling the sense of laser induced unidirectional molecular rotation, one may affect the scattering angle of the molecules. This provides a new means for separation of mixtures of molecules (such as isotopes and nuclear-spin isomers) by laser controlled surface scattering

Modifying molecule-surface scattering by ultrashort laser pulses

In recent years it became possible to align molecules in free space using ultrashort laser pulses. Here we explore two schemes for controlling molecule-surface scattering process, which are based on the laser-induced molecular alignment. In the first scheme, a single ultrashort non-resonant laser pulse is applied to a molecular beam hitting the surface. This pulse modifies the angular distribution of the incident molecules, and causes the scattered molecules to rotate with a preferred sense of rotation (clockwise or counter-clockwise). In the second scheme, two properly delayed laser pulses are applied to a molecular beam composed of two chemically close molecular species (isotopes, or nuclear spin isomers). As the result of the double pulse excitation, these species are selectively scattered to different angles after the collision with the surface. These effects may provide new means for the analysis and separation of molecular mixtures

Measurement of the horizontal velocity of wind perturbations in the middle atmosphere by spaced MF radar systems

Two remote receiving sites have been set up at a distance of approx 40 km from the main MF radar system. This allows measurement of upper atmosphere winds from 60-120 km (3 km resolution) at the corners of an approximately equilateral triangle of side approx 20 km. Some preliminary data are compared through cross correlation and cross spectral analysis in an attempt to determine the horizontal velocity of wind perturbations and/or the horizontal wavelength and phase velocity of gravity waves